1. Field of the Invention
This invention is concerned with adhesive dental restorative composites comprised of thermosetting aromatic and alicyclic polyacrylic resins and inorganic and organic filler materials. Because of their adhesiveness, such restoratives do not require normal cavity preparation and are employed without odontomy procedures.
2. Description of the Prior Art
Diacrylate esters of bisphenolic compounds have been used in the prior dental art for direct filling materials when used in combination with a variety of fillers, and have been used without fillers in the prior art for the sealing of developmental defects.
These resins may contain, as a lesser ingredient in the formulation, either methacrylic acid or short-chain aliphatic diacrylates as reactive diluents. The reactive diluents are frequently added to the basic formulation in order to increase the loading volume of inorganic reinforcing fillers or to facilitate penetration of unfilled systems into developmental defects.
In the formulation of these direct filling materials, the amount of filler employed is critical to satisfactory clinical performance. The fillers are employed at loading volumes of from 70-85%, and serve, by their presence to reduce polymerization shrinkage and thermal expansion rates, such reductions being essential to satisfactory retention of the composites in conventional retentive cavity preparations.
The high concentration of fillers conventionally employed provides satisfactory composites for use in conventional retentive cavity preparations, but because of the paste-like consistency of such composites, they possess poor flow characteristics and tend to consolidate prepared enamel and dentin surfaces less well than the unfilled systems. In addition, the poor flow properties make the attainment of smooth, regular junctions between composites and dentin or enamel difficult, generally requiring substantial cutting and finishing with dental instruments after the composite has cured.
Restorative systems based on unfilled polymethylmethacrylate, while having good flow characteristics, and good consolidation of enamel and regular junctions, must be applied with time-consuming techniques for optimal results in order to minimize polymerization shrinkage. Where polymerized beads of methyl methacrylate were used as filler, such compositions did not flow or wet well. Because neither the composites nor unfilled polymethylmethacrylates of the prior art were particularly suited to the requirements of certain nonoperative restorative procedures, conventional cavity preparations continued to be used.
In the prior art, use of more-or-less lightly filled diacrylates or polymethylmethacrylate systems has been avoided because of the resultant sacrifice of strength properties. Furthermore such lightly filled systems were subject to the filler settling during shipment and storage in the dental office. The resuspension of the fillers was excessively difficult and time consuming. Further, the presence of the fillers prevented the realization of proper flow properties, interfered with wetting and the surface consolidation of prepared tooth structure necessary to prolonged retention in the oral environment.
In the prior art, rods, fibers, and whiskers, primarily but not exclusively of glass, have been employed only in blend with particulate and/or spherical fillers. Apparently the very high loading weights required for composites employed in conventional cavity preparations could not be conveniently achieved with primarily fibrous reinforcement since the viscosity tended to increase out of proportion to the loading weights of fibers employed. Thus the highest strengths in clinically practical systems were attainable only with a combination of fillers rather than with the use of exclusively fibrous reinforcement.
A number of systems have been shown to provide enhanced adhesion to dentin and enamel, but the adhesion is progressively lost with time under the wet conditions in the oral environment. Some of the best reported values have been obtained with special polyurethane systems apparently due to the isocyanate component of the formulation scavenging surface water, which would otherwise adversely influence chemical bonding. Improved bonds have also been achieved with special catalysts for acrylic resins, which likewise react with surface water. It has been demonstrated that greater penetration has been achieved with unfilled polymethylmethacrylate than with the filled composite restoratives. Greater surface consolidation of the enamel and dentin is evidenced by tag-like extensions of the resin into the interstices created by the etchant employed in preparing the surface. Such extensions are not readily disrupted by moisture as chemical bonds are quite often.